The invention provides a semiconductor device including a housing and a semiconductor chip partly embedded in a plastic housing composition, and to a method for producing the same.
The power loss that arises in BGA housings (ball grid array), for example, is not generated with a uniform and constant magnitude over time in most applications. Rather, periods of high power loss are temporally limited and alternate with periods of low power losses. In particular this applies to the customary pulse methods in which no heat loss whatsoever arises in the interpulse intervals. It is only in the active phase of the pulse that a high heat loss arises, which is emitted from the semiconductor chip to the housing. Typical situations for the thermal behavior of a semiconductor device thus arise during these periods of high power losses.
Many solutions for improving the thermal behavior of the plastic housing compositions have already been proposed, but most of these solutions are based on optimizing the static thermal behavior of the housing plastic compositions. Moreover, many of these solutions are very cost-intensive and may reduce the reliability of the housing. Said solutions include for example an integrated heat sink or a heat distributing plate within the housing. This is a cost-intensive solution with additional reliability risks, with the result that the thermal problems can be only partly solved thereby.
Another solution is concerned with so-called underfill materials. The latter are used to fill interspaces between a semiconductor chip and a superordinate circuit board arranged underneath. This is a cost-intensive thermostatic solution that is usually associated with technological problems. Accordingly, the temperature stabilization of semiconductor devices is a constant problem.
As the construction, the speed and the complexity of the semiconductor devices are increasingly improved, increasingly large amounts of heat loss are generated in the semiconductor devices. What is more, the increasing miniaturization of the housings in which semiconductor devices are accommodated provides for a reduction of the possibilities for enabling said semiconductor devices to distribute heat to the surroundings by convection. With increasing miniaturization of the housings it becomes more and more difficult to provide adequate cooling in the surrounding space, especially as the possibility and the efficacy of convection flows are reduced with increasing miniaturization of the housing sizes.
There is additionally the problem of the field of application of these increasingly shrinking semiconductor devices, which nowadays are often incorporated in portable electronic devices such as earphones, portable mobile telephones, portable television sets and also miniature computers and schedulers. The demand for smaller housings produced from lighter materials such as plastics is constantly increasing. These housings are generally lighter than metal housings, but these plastic housings of mobile phones, portable telephones or notebook computers have a higher thermal conduction resistance, with the result that the possibility of dissipating the heat loss of the active semiconductor devices via the housing of these devices has diminished. Consequently, the problem of heat loss dissipation in extremely small devices having electronic semiconductor devices is increasing as the use of plastic housings increases.
Since the reliability of semiconductor devices is associated with the temperature of the devices, many manufacturers of portable electronic systems have conceived of reducing the amount of heat in the semiconductor devices by distributing the heat that is generated within the devices. In particular, it has been attempted to distribute the heat loss within power devices by thermal conduction in order to avoid peak temperatures. Other manufacturers of power devices have attempted to incorporate metallic heat sinks in their power devices, but the efficacy of said heat sinks is very restricted by virtue of the reduction of the available surroundings in the small portable devices for cooling the heat sinks. In addition, the weight of such metallic components for portable electronic devices is neither a contribution for reducing the size nor a contribution for reducing the weight, so that metallic heat sinks within these devices are not very promising.
A further method for reducing the generation of heat loss consists in changing over from an analog design to a digital design. The digital communication systems have therefore substantially replaced analog communication systems, especially as digital systems generally enable improved properties and a generally lower generation of power loss than analog systems, since digital systems operate with a pulse mode. This means that digital systems constantly switch on and off; on the other hand, these pulses may be nested in one another in the form of a plurality of grading systems which can also reduce the total power distribution in a communication system, since these digital systems are operated in only a fraction of the time compared with continuous system.
However, precisely these pulse-operated systems can generate considerable peak power losses during the switched-on pulse. Consequently, rapid power changes may lead to considerably increased thermal stress of the devices during switching on and off. Accordingly, precisely in portable communication systems, the rapid switchover of powers may lead to considerable thermal and mechanical stresses in the semiconductor devices. As a result, circuit connections, wire bonding connections and other mechanical components are severely loaded, which likewise reduces the reliability of these systems. However, since portable electronic devices cannot contain heat sinks for reducing the temperature fluctuations on account of rapid power switching sequences, there is a need to reduce said thermal and mechanical stresses without having to use additional metal heat sinks or heat dissipation arrangements.
For these and other reasons, there is a need for the present invention.